Concrete Cylinder

Brand New Concrete Cylinder

The concrete cylinder is the most common sample type for tests of concrete compressive strength. There are other ways to determine concrete strength, and some methods may be more cost-effective and arguably better, but concrete cylinder testing remains the standard for acceptance.

Well-made concrete cylinders are easy and inexpensive to produce. Typically, one technician posted at the point of discharge or point of placement is sufficient to sample and test concrete batches for the slump, air content, unit weight, and cylinders. Technicians must follow standard practices and be certified in most regions, but training is neither extensive nor complex.

It is essential to understand what concrete cylinder testing is not. Most concrete cylinders cast on the job site are not intended to represent the concrete's in-place strength in the structure. Compressive strength testing of concrete is generally a performance check of the mix delivered to the project. So, as purchased, most field cylinders are made for quality control and product acceptance. The practice for this type of testing is to follow the "standard curing" method found in ASTM C31 / AASHTO T 23. The initial curing environment is controlled and protected, and the samples are retrieved for final laboratory curing within 48 hours. ASTM method C192 / AASHTO R 39 covers test specimens made in the laboratory, where selection, preparation, and mixing of materials are closely controlled to evaluate mix design characteristics.

In cases where it is necessary to monitor strength development in ambient conditions at the job site or within formwork, there are options for "field curing" in the ASTM/AASHTO practice. Instead of adhering to separate temperature and humidity requirements for initial curing, field-cured cylinders undergo the same moisture and temperature conditions as the structural work. In theory, they should reflect the strength development of the concrete in place. This blog post will focus on standard-cure cylinders made for compressive strength acceptance testing.

The equipment for sampling and molding concrete cylinders is simple:

• A wheelbarrow or other container to collect a composite sample of fresh concrete from various types of concrete mixers, as described in ASTM C172. Some project specifications may require sampling at the discharge end of a concrete pump.
• A conveniently sized scoop, large enough to collect a representative sample and small enough for easy handling and fresh concrete placement.
• The specified tamping rod. 4x8in and 6x12in cylinders, each requiring tamping rods with different lengths and diameters.
• A concrete vibrator is also permitted for consolidation and required for stiff mixes with slumps of 1in (25mm) or less.